Effective modulating of the Mo dissolution and polymerization in Ni4Mo/NiMoO4 heterostructure via metal-metal oxide-support interaction for boosting H2 production

Abstract

Constructing low-cost, high-active and robust heterogeneous hydrogen evolution reaction (HER) electrocatalysts with strong metal–metal oxide-support interaction (SMMOSI) is still an urgent challenge for the development of anion exchange membrane water electrolysis (AEMWE), especially under high current density (e.g., 1 A cm−2). Herein, a hierarchical composite of heterogenous Ni4Mo/NiMoO4 (NiMoOx) nanoparticles (NPs) anchored on a mesoporous carbon CMK-3 (NiMoOx@CMK-3) is designed as a superior electrocatalyst for HER. Significantly, the strong interaction between heterogeneous NiMoOx NPs and CMK-3 supporting matrix effectively stabilize the catalytic active Ni4Mo/NiMoO4 heterostructure by altering the local geometric and electronic structures, leading to maximumly exposure of active sites and promoted electron transfer ability. The optimized electrocatalyst exhibits outstanding HER activity with an extremely low overpotential and Tafel slope of 7 mV@10 mA cm−2 and 27.7 mV dec-1, respectively, and can steadily operate at 100 mA cm−2 for 800 h. More significantly, owing to these HER merits, the AEMWE configuration with NiMoOx@CMK-3 (−) is also designed, resulting in low cell voltage of 1.965 V@1 A cm−2 and negligible degradation over 400 h@1 A cm−2. Further ex/in-situ electrochemical spectra evidence that both the partial combined MoO42- from NiMoO4 and the newly formed MoO42- originating from dissolved Mo in NiMoOx@CMK-3 could boost the fast generation of polymerized Mo2O72- that could effectively accelerate the HER process in alkaline conditions by facilitating the formation of active Mo-H* intermediates. Moreover, theoretical calculation results demonstrate the upshifting of d-band center of Mo toward Fermi level for the heterogeneous NiMoOx and the strong charge distribution between the heterointerface could optimize adsorption free energies of H* (ΔGH*) on the surface of Mo atoms.